Orthodontic aid

ABSTRACT

In order to improve the mechanical strength of an orthodontic aid produced on a plastics basis, without having to tolerate any appreciable reduction in the transparency of the bracket, it is suggested that a reinforcement increasing the mechanical strength be arranged at least in those areas acted upon by tooth correction forces, this reinforcement being produced with the use of a ceramic material.

The invention relates to an orthodontic aid, bracket or buccal tube,produced on a plastics basis, comprising a reinforcement increasing themechanical strength and arranged at least in areas acted upon by toothcorrection forces.

Up to now, orthodontic aids, e.g. brackets or buccal tubes made ofmetal, plastics or ceramics have been known which all have theirdiffering advantages and disadvantages. Aids made of plastics areinexpensive and easy to produce and simple to attach to and remove fromthe surfaces of the patient's teeth. A disadvantage of these aids is thefact that they are pliable in the areas, in which they are acted upon bytooth correction forces, and so they do not allow any exact control ofthe tooth displacement to be carried out.

Metallic, orthodontic aids have the disadvantage that the aids are veryconspicuous due to the metallic gleam of the parts and their silverycolour and they give the patient undergoing treatment a so-called"metallic smile".

Ceramic parts, in particular produced from alumina, are considerablyless conspicuous in the mouth of the patient than the metallic brackets.They do, however, have the disadvantage that they are very hard and poseproblems during removal from the surface of the teeth after successfultreatment.

In order to at least partially obviate the problems with the bracketsproduced on a plastics basis, it has already been suggested that thesebe provided with a metal insert in order to improve the stiffness of thebracket and also its mechanical strength. The metallic inserts do,however, cause a reduction in the transparency of the bracket and sothis is just as noticeable in the mouth of the patient as metallicbrackets. Moreover, when the metallic inserts lie exposed on the surfaceof the aid, they exhibit, in the same way as the metallic brackets, toogreat an abrasion and too great a friction with the arch wiresgenerating the correction forces.

The object of the invention is to avoid the aforesaid disadvantages inan orthodontic aid of the type described at the outset.

This object is accomplished in accordance with the invention, in abracket of the type described at the outset, in that the reinforcementis produced with the use of a ceramic material.

Despite the extremely large differences in the heat expansion and in themodulus of elasticity of conventional plastics and ceramic materials,surprisingly no problems arise at the transitions between materials.This is especially unexpected since, when the aids are worn in the mouthof the patient, a vast number of hot-cold cycles occur daily, forexample when drinking hot or cold beverages or consuming hot meals orice cream.

Oxide ceramic material is particularly suitable. In this respect, twosolutions are in principle conceivable, namely, on the one hand, the useof the ceramic material as filler for the plastic of the plastic bracketin the mechanically stressed parts or, on the other hand, its use asstarting product for the manufacture of an insert element for themechanically stressed parts of the bracket.

The use of the oxide inorganic masses in the production of thereinforcement (in the following generally referred to as ceramics)reduces the abrasion and diminishes the friction of the arch wireinserted in the slot of a bracket. Preferably, the reinforcementessentially forms the surface regions of the aid which are acted upon bythe correction forces.

The ceramic mass may be produced transparent or at least opaque and, forthis reason, the aesthetic requirements to be met by the orthodonticaids are better fulfilled. Normally, a difference in colour to theplastic material can scarcely be ascertained. In comparison with thebrackets which consist completely of ceramics, the risk of breakageduring the removal of the bracket from the patient's tooth is avoided,and also the problems involved with the bonding of the ceramic bracketsto the tooth surface, since the inventive orthodontic aids, like theknown aids which consist altogether of plastic and are not reinforced,can be attached and removed in a known manner.

The reinforcement preferably comprises a ceramic part, in particularmade of sintered, polycrystalline alumina. In the case of this material,the transparency or translucency of the part, in particular, can beadapted very well to the transparency or translucency of the surroundingplastic material. The plastic material is preferably adapted in itscolour, and therefore the reinforcement part as well, to the colour ofthe teeth, possibly even individually to the colour of the teeth of theparticular patient.

The ceramic part of the reinforcement can be held in a force fit in theaid, whereby the aid and the reinforcement part are then producedseparately and not joined together until a further operating process.

The actual aid part can just as easily be sprayed onto a prefabricatedceramic reinforcement part. However, the reinforcement part can, ofcourse, also be bonded to the plastic aid.

Alternatively to a ceramic part, the reinforcement can be a polymer partfilled with particulate ceramic material. This can be producedindependently of the orthodontic aid or be designed in one piece withit. The separately produced reinforcement can, again, be held in a forcefit in the orthodontic aid or be bonded thereto. It is also possible inthis case for the aid to be sprayed onto the reinforcement.

Preferably, the plastic, from which the orthodontic aids are made, willcomprise a polyethylene, polyester, polycarbonate or polyacrylic resinportion or copolymer portions derived herefrom.

The particulate, ceramic material for reinforcing the polymer parts willpreferably comprise essentially ZrO₂ or silicon dioxide, in particularin the form of powdered quartz or cristobalite, or even alumina,especially in its trihydrate form.

Alumina trihydrate has the advantage over silicon dioxide that it isless hard and therefore no metal abrasion, for example from the archwire, takes place, i.e. metal parts rubbing on the reinforcement partsdo not lead to so-called writing traces which can give the part a greyor dull and therefore conspicuous appearance.

The average particle size of the filler material is preferably selectedto be in the range of between 5 μm to 100 μm since, on the one hand, theparticles of this size can easily be stabilized in the mixture providedfor the manufacture of the reinforcement part and, on the other hand, anadequate surface smoothness of the produced reinforcement part isensured. The proportion of the ceramic material in the overall mass canbe very high, i.e. 50-80% by weight.

A bracket, which is equipped with a base for direct bonding of the aidto a surface of a tooth, can, in particular, be considered as areinforced, orthodontic aid. The reinforcement is then designed suchthat the strength of the base is essentially not influenced. Thislimitation of the reinforcement parts to the areas of the bracketreceiving the forces is important, in particular, with a view to thelater removal of the brackets from the tooth surface since, in the caseof the otherwise flexible plastic brackets, a gradual separation of thebracket base from the point of bonding on the tooth surface may becarried out. The forces which act on the tooth at any point of timehereby remain so slight that no tears can occur in the tooth enamel onthe tooth surface.

The removal of the brackets from the tooth surface can be carried outwith simple pliers-type instruments, as already known from previousplastic brackets.

The reinforcement of the bracket is limited, in particular, to thatregion of the slot provided for accommodating an arch wire, via whichthe correction forces of the arch wire are transferred to the bracketand, finally, to the tooth.

An additional, alternative embodiment of the invention consists in thefact that the aid, in particular the bracket, is produced altogetherfrom a plastic filled to a considerable extent with particulate ceramicmaterial. In this case, as in the variant described in the above, theproduction method as well as the selection of material for the highlyfilled plastics is known from the field of sanitation technology. Forexample, DE-PS 24 49 656 and U.S. Pat. No. 3,847,865 are cited.

Although sanitation technology deals with a quite different set ofproblems to those of orthodontic aids, the material described in thiscase can surprisingly and advantageously be used, modified if necessary,in orthodontics. It is particularly surprising to find that the materialwhich is known in sanitation technology only for objects having largesurfaces, such as e.g. baths or also kitchen worktops, can be utilizedwithout problem for the production of very small and relatively complexstructures.

These and additional advantages of the invention are explained ingreater detail in the following on the basis of the drawings. Thesedrawings show in detail, in

FIG. 1 an inventive orthodontic aid in the form of a bracket having aninserted reinforcement;

FIG. 2 an inventive orthodontic aid in the form of a bracket having anintegrally designed reinforcement.

FIG. 1 shows an orthodontic aid in the form of a bracket and designatedas a whole with the reference numeral 10. This is customarily used inorthodontics for performing corrections to the position of teeth.

The bracket has an underside or base 12, with which it can be bonded toa surface of a tooth.

A slot 14, which is essentially rectangular in cross section, isprovided in the longitudinal direction and on the upper side. An archwire, which applies the correction forces for altering the position ofteeth to the bracket, is inserted into this slot.

In addition, so-called tie wings 16 are provided on both sides of theslot 14 and these form a support for attachment means for the arch wire.The arch wire can be held securely in the slot 14 with the attachmentmeans and this ensures over the treatment period that the correctionforces always act on the tooth in the manner desired by the dentist incharge.

The special inventive characteristic of the bracket 10 illustrated inFIG. 1 is to be seen in the reinforcement of the bracket in the regionof the slot 14, whereby in the embodiment shown in FIG. 1 areinforcement part 18 is inserted which extends over the entire lengthof the slot 14. Alternatively, it is possible for the reinforcement part18 to be designed somewhat shorter than the slot 14 and be covered atits end faces by the plastic material of the remaining bracket body. Thereinforcement part 18 consists, in this case, of sintered,polycrystalline alumina and has very similar colour and translucencyvalues to the surrounding plastic material of the bracket 10.

The bracket, when attached to the tooth, differs in its appearance onlyinsignificantly from the purely plastic brackets, i.e. it remainsessentially invisible when worn by the patient. Nevertheless, aconsiderable improvement in the accuracy of the tooth correctionachieved is obtained with the inventive bracket since the correctionforces are transferred over considerably larger surfaces to the bracketbody due to the insert of the reinforcement part 18 in the bracket 10,without any deformation of the slot 14 hereby resulting.

In the embodiment shown in FIG. 1, the side walls of the reinforcementpart 18 reach as far as the upper side of the bracket 10. Alternativelyto this, it would also be possible to design the side walls to besomewhat: lower, whereby they are then covered in the region of theupper side of the bracket by the plastic material of the bracket body.It is important for the reinforcement part 18, with a view to minimizingthe friction between arch wire and bracket in the region of the slot 14,that those surface regions of the slot 14, which come into contact withthe arch wire and via which the correction forces for the teeth areconveyed from the arch wire onto the bracket, are formed by thereinforcement part 18.

FIG. 2 shows an alternative embodiment of the invention, also on thebasis of a bracket 20, whereby, as in the bracket described in FIG. 1, aslot 22 is provided for receiving an arch wire, which is not shown, aswell as so-called tie wings 24 which serve to fix the arch wire inposition in the slot 22. The bracket is, like the bracket of FIG. 1,bonded with its underside or base 26 to the tooth surface of the teethof the patient undergoing treatment.

In contrast to the embodiment of FIG. 1, the slot 22 is, however, notlined with a separate reinforcement part but rather the plastic materialof the bracket 20 is mechanically reinforced by the introduction incertain areas of inorganic, oxide material, in particular alumina in itstrihydrate form, to such an extent that it has, with respect to thetransfer of correction forces from the arch wire to the bracket body,altogether the same effect as the insert 18 in FIG. 1. At the same time,friction with the metallic arch wire is approximately equally as low.

The inventive brackets described above may, of course, be bonded ontotapes and not only directly onto the tooth surface. The advantages ofthe inventive brackets as described do, of course, remain the same.

I claim:
 1. An orthodontic aid for transferring tooth correcting forcessupplied by an arch wire to a tooth comprising a substantially plasticbody having a lower surface and an upper surface, the lower surfaceforming a base for bonding the plastic body to the tooth, the uppersurface having a slot for receiving the arch wire and attachment meansfor holding the wire in the slot; and a reinforcement produced using aceramic material and held in a force fit in the slot for increasing themechanical strength of the plastic body where it is acted upon by thetooth correcting forces.
 2. An orthodontic aid as defined in claim 1,wherein the ceramic material comprises an oxide ceramic material.
 3. Anorthodontic aid as defined in claim 1, wherein the ceramic materialcomprises sintered polycrystalline alumina.
 4. An orthodontic aid asdefined in claim 1, wherein the reinforcement comprises a plastic partcontaining particulate ceramic material.
 5. An orthodontic aid asdefined in claim 4, wherein the particulate ceramic material compriseszirconia.
 6. An orthodontic aid as defined in claim 4, wherein theaverage particle size of the ceramic material is approximately 5 μm to100 μm.
 7. An orthodontic aid as defined in claim 4, wherein theparticulate ceramic material comprises silicon dioxide.
 8. Anorthodontic aid as defined in claim 4, wherein the particulate ceramicmaterial comprises alumina.
 9. An orthodontic aid as defined in claim 1,wherein the reinforcement is disposed within the slot between the archwire and the plastic body for transferring correction forces from thearch wire to the aid.
 10. An orthodontic aid as defined in claim 1,wherein the reinforcement comprises a translucent material.
 11. Anorthodontic aid as defined in claim 1, wherein the plastic bodycomprises a polycarbonate resin.
 12. An orthodontic aid as defined inclaim 1, wherein the reinforcement strengthens the slot of the plasticbody for interaction with the arch wire without altering the mechanicalproperties of the base.
 13. An orthodontic aid as defined in claim 1,wherein the plastic body comprises a polyethylene resin.
 14. Anorthodontic aid as defined in claim 1, wherein the plastic bodycomprises a polyester resin.
 15. An orthodontic aid as defined in claim1, wherein the plastic body comprises a polyacrylic resin.
 16. Anorthodontic aid as defined in claim 1, wherein the plastic bodycomprises a copolymer derived from a combination of at least two of thegroup consisting of polycarbonate, polyethylene, polyester orpolyacrylic resin.